The invention relates to the field of hydrodynamic bearings in electric motors. More specifically, the invention relates to a method for setting the gaps in the hydrodynamic bearings in electric motors utilized in a disk drive system.
Disc drive memory systems have been used in computers for many years for storage of digital information. Information is recorded on concentric memory tracks of a magnetic disc medium, the actual information being stored in the form of magnetic transitions within the medium. The discs themselves are rotatably mounted on a spindle. The information is accessed by using read/write heads generally located on a pivoting arm that moves radially over the surface of the disc. The read/write heads or transducers must be accurately aligned with the storage tracks on the disc to ensure proper reading and writing of information.
During operation, the discs are rotated at very high speeds within an enclosed housing by using an electric motor generally located inside a hub that supports the discs. One type of motor in common use is known as an in-hub or in-spindle motor. Such in-spindle motors typically have a spindle mounted using two ball or hydrodynamic bearing systems to a motor shaft disposed in the center of the hub.
In a hydrodynamic bearing, a lubricating fluid such as air, gas or oil provides a bearing surface between two relatively rotating members, typically a shaft and surrounding sleeve. A volume containing the lubricating fluid is typically held between the hydrodynamic bearings. Each bearing is positioned proximate an end of the shaft and is spaced apart from the rotor hub by a small gap. To effectively form hydrodynamic bearings, the volume of fluid must be consistently and accurately formed. As such, the gap between the bearings and the rotor hub must be repeatable from disc drive to disc drive in the manufacturing process.
Therefore, there is a need in the art for a method that can accurately and repeatably set these gaps while allowing for high-speed assembly.
A method for setting a gap in a hydrodynamic bearing of a disc drive spindle motor is provided. The invention comprises mounting a rotor hub having a central journal sleeve onto a shaft that has been secured to a support after having had a lower thrust bearing pressed onto the shaft in communication with the support, adding an amount of hydrodynamic fluid into the rotor hub""s journal sleeve, pressing an upper thrust bearing onto the rotor shaft until contact is made with the rotor hub, and rotating the hub until axial forces balance and set the air and fluid bearing.
While rotating, the rotor hub generates a pressure force that forces the hydrodynamic fluid disposed around the base of the shaft to move up the shaft. As the pressure force builds, a layer of air between the upper bearing and the fluid builds up pressure, the layer of air is forced between the upper shaft bearing and the rotor hub. The pressure forces the rotor hub to move until the air pressure equals the fluid pressure. This invention is especially useful in disc drive spindle motors, in that it provides a more efficient way of assembling a disc drive spindle motor because of the significant reduction of steps for manufacturing the prior art hydrodynamic bearings commonly found in disc drive spindle motors. Additionally, the invention may be useful for setting gaps in the hydrodynamic bearings of other types of motors. The invention can be used in both conical type hydrodynamic bearings and flat/thrust plate bearings.